The present invention is with respect to gravure printing machine cylinders having means for mounting and tensioning wrap-on plates, using a tensioner that is able to be rocked about the shaft of the cylinder and has an outer surface in keeping with the plate supporting radius or outline of the cylinder.
In the case of known plate mounting or fixing means of this sort the tensioner has to be rocked through a relatively large angle about the shaft of the cylinder in order to get the axis-parallel ends of the plate, that are in the form of bent-back folds or have slats fixed thereto, fitted on the edge, that is in the front in the direction of tensioning, of the tensioner. This has an undesired effect on the load supporting power or strength of the back end of the tensioner in the joint. This shortcoming is more specially serious when the end of the plates have mounting folds that are very long and are bent back at an acute angle.
Gravure printing machine cylinders have furthermore been designed with a plate mounting system whose tensioner is only able to be rocked about an axis which is eccentric in relation to the shaft of the cylinder so that the edge which is leading (with respect to the direction of tightening the plate) may be moved inwards and outwards in the radial direction. Although on the one hand this makes it simpler for the fold of the plate to be mounted, on the other hand this sort of mounting means makes it necessary for the plates to be made highly true to size, that is to say, to keep to tight production tolerances. The reason for this is that in the case of these known systems there is only one given working position of the tensioner, in which the outer face or form of the tensioner is centered on the axis of the cylinder, that is to say so that the outer faces of the tensioner and of the rest of the cylinder are co-cylindrical. In other words, as long as the tensioner is not in this position, it will be at an angle in relation to the rest of the outer face of the cylinder with part thereof at a greater radius from the cylinder axis and part thereof at a smaller radius from the axis than the said rest of the outer face of the cylinder. In fact, if the wrap-on plate to be mounted is overlong or overshort because of manufacturing tolerances, the tensioner will then not be able to be rocked into its true co-cylinderical position and will keep in a position with the two circumferential ends thereof forming steps or ledges with the ends of the rest of the outer part of the cylinder. Such steps wil be the cause of the impression cylinder and the doctor sharply kicking against the plate cylinder where the steps are and vibration being caused so that ink is likely to be splashed onto the paper or stripes formed thereon. And there is furthermore a chance of the paper tearing because of the force acting thereon.